Weekly update from AVO

2009-06-26 12:51:07 - Weekly Update
Growth of the lava dome at Redoubt volcano has significantly slowed. Seismicity remained low during the past week, but is still above background. Poor weather conditions during the last two weeks have prevented fieldwork and all but an occasional glimpse of the lava dome and steam plume by the web cameras. These glimpses, the continued low level of seismicity, and consistent lower gas emissions suggest that growth of the lava dome has significantly slowed. Redoubt remains at Orange/Watch as AVO continues to assess activity.

The last aerial observations were made on Monday, June 15. The lava dome is approximately 1,000 m in length, 460 m in width, and 200 m tall. This large mass of fresh lava may still be unstable and could fail with little or no warning, leading to significant ash production and possible lahars in the Drift River valley.

AVO continues to monitor Redoubt's activity 24/7. AVO will provide frequent updates of the volcano's status and the earliest possible warning of significant explosive activity and other hazards.

Redoubt alert codes lowered to YELLOW/Advisory.
Update from AVO

2009-06-30 10:20:03 - VAN/VONA
AVO is lowering the Aviation Color Code to Yellow and the Alert Level to Advisory at Redoubt volcano. Seismic, satellite, gas, and deformation observations over the past few weeks indicate that growth of the lava dome at Redoubt has significantly slowed, if not stopped, and therefore it is possible that the current eruptive activity has ended. However, it is unknown if this represents the end of the 2009 eruption of Redoubt or if the activity has only paused temporarily and might resume in the next months.

The large lava dome located at the north side of the summit crater, and extending down the Drift Glacier Gorge, still presents a hazard. It is possible that this large mass of fresh lava is unstable and could fail with little or no warning, leading to significant ash production and possible lahars in the Drift River valley.

AVO will continue to monitor Redoubt's activity closely, but begin to transition off 24/7 staffing. Later updates will describe operational changes as they occur.

Information statement from AVO.
Long but interesting!

Extended Information Statement

Summary

The 2009 eruption of Redoubt volcano began March 15th, 2009 with a steam explosion. Between March 22nd and April 4th, Redoubt produced multiple significant explosions that sent ash and gas clouds to as high as 65,000 feet (19.8 km) above sea level. After April 4th, the eruption continued with extrusion of a lava dome within the summit crater, eventually producing a blocky lava flow that currently extends ~0.6 miles (1 km) down the north flank of the volcano. Redoubt entered its 14th week of eruptive activity the week of June 22nd.

Observations from overflights, webcam, and satellite imagery have not been able to detect changes caused by dome growth for the past three weeks, thus lava effusion has at least slowed significantly, and may have stopped. Consequently AVO downgraded the aviation color code to YELLOW and the alert level to ADVISORY on Tuesday June 30th, 2009. Volcanic seismicity is still reduced, after a decline in the numbers of earthquakes per day began about May 7th. However, seismicity remains elevated above background. Volcanic gas emissions remain very high, yet have also decreased by about half since early-May. AVO will continue to monitor Redoubt's activity closely, but will begin to transition off 24/7 staffing. Later updates will describe operational changes as they occur.

Despite evidence for the significant slowing, and possible cessation of its growth rate, the lava dome is potentially unstable and the possibility of a full or partial collapse remains high at present. Such a collapse would likely be accompanied by the production of a large ash plume and lahars in the Drift River valley. This event could occur with little or no advance warning.

Recent Observations

As of June 9th, the lava dome is approximately 67.5 million m3 in volume, estimated from analyses of visible and infrared photographs. The lava dome is now larger than any produced during the 1989-90 eruption. The dimensions of the dome have not increased perceptibly over the past 3 weeks, and are estimated to be 1000 m (3280 ft) long (north-to-south) 460 m (1510 ft) wide (east-to-west) and 200 m (655 ft) tall. Rock fall from the slopes of the dome continues, though at a lower rate than the previous month. Recent thermal measurements made during helicopter overflights indicate that most of the lava dome surface is relatively cool (~90°C or less), while smaller, hotter regions reveal much higher interior temperatures (>250°C). The measurements reflect the temperature of the cooling lava and do not represent the actual lava temperature as it emerges from the vent. Temperatures of fresh lava of this composition should be considerably higher (~850 to 950°C).

Seismic activity at Mount Redoubt has declined over the past month, but remains elevated above background levels. Generally, fewer than 6 earthquakes per day have been recorded at Redoubt during the past two weeks. Normal background rates of earthquake occurrence at Redoubt are typically fewer than four located earthquakes each month, which is a significantly lower rate of occurrence than what AVO observes at this time. A M3.1 event did occur ~6 km east to northeast of Redoubt's summit the morning of Tuesday June 30th, also showing that the volcano remains seismically active at this time. Seismicity during the past month comprises small, discrete events and occasional signals from rock falls off the slopes of the unstable dome. Some rock falls have generated diffuse, low-level ash clouds in the summit region and minor ash deposits around the dome.

Geodetic data indicate that deflation of the volcanic edifice has also slowed over the past month. A change in this trend towards renewed inflation could signify unrest leading to renewed eruptive activity.

Airborne gas measurements indicate that Redoubt's emissions remain very high and are currently still at levels typical for an erupting volcano, yet they have declined measurably over the past couple of weeks. These gas emissions are consistent with degassing expected from the lava extrusion that continued through early June. Using past eruptions at Redoubt and other andesitic volcanoes (Augustine and Mount St. Helens) as a reference, we expect the emissions to continue to decline slowly over a period of several months as already-erupted magma degasses.

Prognosis and Ongoing Hazards

The current lava dome has been in place since the last explosive event occurred on the morning of April 4th. For most of this time it grew at a rate that was easily noticed and measured using a combination of satellite- aircraft- and ground-based imaging systems. The growth was accompanied by morphologic changes, frequent rockfall, and cracking of the outer cool skin, exposing incandescent viscous lava. By June 9th effusion of magma had slowed at least to the point that we are unable to detect any further growth, and may have stopped. As of this writing there have been 87 days of uninterrupted growth. This contrasts with a maximum of 36 days of dome growth between significant explosive events in 1990, apart from the final 1990 dome, which was stable for nearly 19 years and was destroyed at the onset of the current eruption.

Declining seismicity and gas emissions also indicate a decline or cessation of eruption. Based on our current observations at Redoubt volcano, and understanding of prior eruptions, AVO considers the following future scenarios as possible:

1) Continued decline in seismicity and gas emissions with no measureable output of lava leading to an end of the eruption and a return to background.
2) Renewed explosive activity triggered by sealing of the conduit and the resulting buildup of gas overpressure, or as a result of fresh magma ascending into the shallow conduit beneath Redoubt.
3) Renewed lava dome growth, caused by increase in magma extrusion rate.

Based on all available monitoring data, AVO considers scenario number 1, waning lava dome growth leading to the end of the eruption, as the most probable outcome at this time. The most likely hazard related to scenario 1 would result from collapse or failure of the lava dome due to gravitational instability. This could happen with little to no warning, and would likely cause an ash cloud to form in association with the resulting hot block and ash flow, as well as lahars that could significantly impact the Drift River valley. Based on the progression of events after cessation of lava dome growth during the 1989-1990 eruption of Redoubt, it is also possible that small steam explosions and continued rock fall events could occur within the immediate vicinity of the summit crater and upper Drift glacier valley.

Although it is considered less likely at this time, renewed explosive activity could also occur (scenario 2), triggered by a build up of gas overpressure as a result of sealing of the conduit. This could be caused either by gas pressurization from continued magma degassing, or as a result of new magma ascending in the conduit beneath Redoubt. Alternatively, the lava dome growth rate could increase in response to an increase in the effusion rate of magma from the shallow system beneath Redoubt (scenario 3). Given the large size of the present lava dome, increased lava dome growth could also lead to failure due to over-steepening of the dome. Either scenario 2 or 3 (or a combination of the two) would likely generate a flow of hot lava blocks and ash down the north slope of the volcano, and a significant ash cloud to elevations of 30,000 feet or more above sea level. Flooding of the Drift River valley would also be a likely outcome. It is likely that renewed activity leading to scenario 2 or 3 would be preceded by a measurable increase in seismic or other unrest, which would bring AVO back to full alert. However, it is also possible that renewed explosions or extrusion could occur with little or no warning.

Weekly update from AVO:

2009-07-03 13:06:54 - Weekly Update
Continued low seismicity, reduced gas emissions, and lack of observable growth in the lava dome suggest that the 2009 eruption of Redoubt may be drawing to a close. Due to this consistent trend in the data, AVO lowered Redoubt's Aviation Color Code from Orange to Yellow, and the Alert Level from Watch to Advisory on Tuesday, June 30. The 1 km-long lava dome at the summit, however, remains potentially unstable. Collapse of the lava dome would likely result in high-level ash production, hot lava block and ash flows, and possible flooding in the Drift River valley.

Web camera views, when clear, show continued steaming at the summit.

AVO scientists conducted field work at Redoubt this week, including measuring gas emissions from the steam and gas plume, observing the lava dome, collecting thermal imagery of the dome, and maintaining field equipment.

AVO will continue to monitor Redoubt's activity closely, but will begin to transition off of 24/7 staffing.

Information Statement from AVO:

2009-07-09 13:46:18 - Information Statement
As of today, July 9, AVO is standing down from 24/7 staffing of its operations center. AVO will have someone on duty in the office from 6 am to 9 pm seven days a week, but a staff scientist may not be in the operations center to immediately answer phone calls. At times we may not respond to inquiries as quickly as we have over the past several months, but will return phone calls or requests for information as soon as possible.

It is still possible for conditions at the volcano to change rapidly and seismic activity or other signs of unrest could escalate over time periods as short as 24 hours or less. The lava dome in the summit crater has not yet fully stabilized and may completely or partially collapse with little or no advance warning. A significant dome collapse would likely result in the production of hazardous ash clouds, possibly to aircraft flight levels, hot block and ash flows, and flooding in the Drift River valley. AVO will monitor for such activity on a 24/7 basis using alarms that send notifications to on call staff who will be able to respond quickly. AVO scientists will continue to examine monitoring data regularly and report on activity through our daily status reports and weekly updates.

AVO staff can be contacted by calling 907-786-7497. If no one answers at this number, calls will be forwarded to an answering service that will put you in contact with an AVO scientist. Usually, someone from AVO is able to respond to such calls within 10 minutes.

Weekly update:

2009-07-10 12:13:03 - Weekly Update
No significant changes have been observed at Redoubt Volcano over the past week. Seismicity at the volcano has been slightly above background throughout the week and web camera views show continued steaming from the lava dome. The lava dome does not appear to be growing, but because of its size and location at the head of a steep bedrock canyon, it is potentially unstable, and could collapse with little or no warning. A major dome collapse event would likely result in significant ash production, with ash plumes possibly rising to aircraft flight levels, hot block and ash flows, and flooding in the Drift River valley.

Yesterday AVO suspended 24/7 staffing of its operations center due to the diminished activity at Redoubt. AVO continues to monitor the volcano on a 24/7 basis using an alarm system that alerts on call staff of unrest, who then can respond accordingly.

Can you explain this "dome" to me?
2dn line

When lava erupting from a volcano is very viscous, it doesn't flow away like a liquid (like usually happens for example in Hawaiian volcanoes), but remains close to the eruption vent like if it had jam consistency. Over time, depending on the eruption rate, such viscous lava accumulates and eventually becomes a semisolid mass of typically hemispherical shape (thus, "dome").

Although they may appear stable and cool (since they usually don't really "glow"), lava domes are actually inherently unstable and very hot inside (600-800 degrees celsius) and can collapse under they own weight any time, generating in the process very hot flows of ash and rocks and also explosions in some cases due to trapped gases bursting out with violence. This hazard grows in probability over time as the dome size increases.

The current Redoubt lava dome is very big and is on a rather steep slope. It hasn't cooled off completely yet, so it can collapse totally or partially any time. The probability of this happening though, appears to be diminishing over time. More than two months have passed since the last dome collapse, and the current one is not growing anymore. Given enough time, the dome can cool off, compact itself in the solidifying process, and eventually stabilize.

By comparison though, the remnant dome of the 1989-1990 Redoubt eruption, was very very small.

Last time I checked, AVO said that most volcano data (GPS, seismic, lava dome temperature, gas emissions, etc) indicates that the eruption is most probably nearing to an end without any further catastrophic events. Still, the dome could collapse any time and energetic volcanic activity could start again without prior notice. So, nothing is certain yet.

Weekly update from AVO:

2009-07-17 11:49:16 - Weekly Update
No significant changes have been observed at Redoubt volcano this week. Seismicity remains low, and clear web camera views throughout the week show steaming from the lava dome. More vigorous steaming was observed on Wednesday prompting concern from the public although no ash signals have been observed in radar or satellite data. The hot, lava dome remains potentially unstable, and could collapse with little or no warning. A collapse would likely result in significant ash production, hot block and ash flows, and flooding in the Drift River valley.

Although the operations center is not manned 24/7, AVO continues to monitor the volcano on a 24/7 basis using an alarm system that alerts on-call staff of unrest, who then can respond accordingly.

It looks like the bad weather front has reached Redoubt Volcano as showed by many webicorders in the AVO website (especially RSO). By looking more in detail at seismic data though (again, especially RSO, since it's the closest station to the summit) it appears to me that mixed with weather induced seismic noise there is also indication of increased rockfalls/dome erosion seismic signals compared to previous days.

Since the current Redoubt lava dome is still potentially unstable it might be worth to keep an eye on it - the harsh weather could be making a dome collapse possibility more likely than before.

I think something is happening at Redoubt at the moment. There's bad weather, but also other signals mixed with small earthquakes that make me think that the current lava dome is about to collapse. Stay tuned!

Weekly update from AVO. Sulfur dioxide emissions (one of the main indicators of active volcanism) are diminishing, but are still above normal levels:

2009-08-14 13:50:27 - Weekly Update
No significant changes have been observed at Redoubt volcano this week. Seismicity remains low. Clear weather earlier in the week allowed for satellite observation of a continued thermal anomaly at Redoubt. Web camera views showed continuing steam and gas emissions. Data collected on a gas and observation flight on August 3 indicate a slight decrease in the emissions of SO2 at the volcano although the emission rates are still considered to be above background. The lava dome is cooling and remains potentially unstable. It could collapse with little or no warning. A collapse would likely result in significant ash production, hot block and ash flows, and flooding in the Drift River valley.

Although the operations center is not staffed 24/7, AVO continues to monitor the volcano on a 24/7 basis using an alarm system that alerts on-call staff of unrest, who then can respond accordingly.

Heavily ice-mantled Redoubt volcano is located on the western side of Cook Inlet, 170 km (106 mi) southwest of Anchorage and 82 km (51 mi) west of Kenai, within Lake Clark National Park. Redoubt is a stratovolcano which rises to 10,197 feet above sea level. Recent eruptions occurred in 1902, 1966-68, 1989-90, and 2009. The 1989-90 and 2009 eruptions produced mudflows, or lahars, that traveled down the Drift River and partially flooded the Drift River Oil Terminal facility. The ash plumes produced by the 1989-90 and 2009 eruptions significantly disrupted air traffic and resulted in minor or trace amounts of ash in the city of Anchorage and other communities in south-central and interior Alaska.